Microsoft generally releases MSRT monthly as part of Windows Update or as the standalone tool. Use this tool to find and remove specific prevalent threats and reverse the changes they have made (see covered threats). For comprehensive malware detection and removal, consider using Microsoft Safety Scanner.

This article contains information about how the tool differs from an antivirus or antimalware product, how you can download and run the tool, what happens when the tool finds malware, and tool release information. It also includes information for the administrators and advanced users, including information about supported command-line switches.

Note In compliance with the Microsoft Support Lifecycle policy, MSRT is no longer supported on Windows Vista and older platforms. For more information, go to Microsoft Support Lifecycle.

More Information

The Malicious Software Removal Tool does not replace an antivirus product. It is strictly a post-infection removal tool. Therefore, we strongly recommend that you install and use an up-to-date antivirus product.

The Malicious Software Removal Tool differs from an antivirus product in three key ways:

The tool removes malicious software from an already-infected computer. Antivirus products block malicious software from running on a computer. It is significantly more desirable to block malicious software from running on a computer than to remove it after infection.

The tool removes only specific prevalent malicious software. Specific prevalent malicious software is a small subset of all the malicious software that exists today.

The tool focuses on the detection and removal of active malicious software. Active malicious software is malicious software that is currently running on the computer. The tool cannot remove malicious software that is not running. However, an antivirus product can perform this task.

Note The Malicious Software Removal Tool focuses on the detection and removal of malicious software such as viruses, worms, and Trojan horses only. It does not remove spyware. However, you can use Microsoft Security Essentials to detect and remove spyware.

You do not have to disable or remove your antivirus program when you install the Malicious Software Removal Tool. However, if prevalent, malicious software has infected your computer, the antivirus program may detect this malicious software and may prevent the removal tool from removing it when the removal tool runs. In this case, you can use your antivirus program to remove the malicious software.

Because the Malicious Software Removal Tool does not contain a virus or a worm, the removal tool alone should not trigger your antivirus program. However, if malicious software infected the computer before you installed an up-to-date antivirus program, your antivirus program may not detect this malicious software until the tool tries to remove it.

The easiest way to download and run the tool is to turn on Automatic Updates. Turning on Automatic Updates guarantees that you receive the tool automatically every month. If you have Automatic Updates turned on, you have already been receiving new versions of this tool monthly. The tool runs in quiet mode unless it finds an infection. If you have not been notified of an infection, no malicious software has been found that needs your attention.

Enabling automatic updates

To turn on Automatic Updates yourself, follow the steps in the following table for the operating system that your computer is running.

Select Advanced options, and then under Choose how updates are installed, select Automatic (recommended).

Note Windows 10 is a service, which means automatic updates are turned on by default and your PC always has the latest and best features.

Windows 8.1

Open Windows Update by swiping in from the right edge of the screen (or, if you're using a mouse, pointing to the lower-right corner of the screen and moving the mouse pointer up), select Settings > Change PC settings > Update and recovery > Windows Update. If you want to check for updates manually, select Check now.

Select Choose how updates get installed, and then under Important updates, select Install updates automatically (recommended).

Under Recommended updates, select the Give me recommended updates the same way I receive important updates check box.

Under Microsoft Update, select the Give me updates for other Microsoft products when I update Windows check box, and then select Apply.

Windows 7

Click Start, point to All Programs, and then click Windows Update.

In the left pane, click Change settings.

Click to select Install updates automatically (recommended).

Under Recommended updates, click to select the Give me recommended updates the same way I receive important updates check box, and then click OK. If you are prompted for an administrative password or for confirmation, type the password or provide confirmation. Go to step 3.

Video: How to turn on Automatic Updates in Windows 7

Download the Malicious Software Removal Tool. You must accept the Microsoft Software License Terms. The license terms are only displayed for the first time that you access Automatic Updates.

Note After you accept the one-time license terms, you can receive future versions of the Malicious Software Removal Tool without being logged on to the computer as an administrator.

The Malicious Software Removal Tool runs in quiet mode. If it detects malicious software on your computer, the next time that you log on to your computer as a computer administrator, a balloon will appear in the notification area to make you aware of the detection.

Performing a full scan

If the tool finds malicious software, you may be prompted to perform a full scan. We recommend that you perform this scan. A full scan performs a quick scan and then a full scan of the computer, regardless of whether malicious software is found during the quick scan. This scan can take several hours to complete because it will scan all fixed and removable drives. However, mapped network drives are not scanned.

Removing malicious files

If malicious software has modified (infected) files on your computer, the tool prompts you to remove the malicious software from those files. If the malicious software modified your browser settings, your homepage may be changed automatically to a page that gives you directions on how to restore these settings.

You can clean specific files or all the infected files that the tool finds. Be aware that some data loss is possible during this process. Also, be aware that the tool may be unable to restore some files to the original, pre-infection state.

The removal tool may request that you restart your computer to complete the removal of some malicious software, or it may prompt you to perform manual steps to complete the removal of the malicious software. To complete the removal, you should use an up-to-date antivirus product.

Reporting infection information to Microsoft

The Malicious Software Removal Tool will send basic information to Microsoft if the tool detects malicious software or finds an error. This information will be used for tracking virus prevalence. No identifiable personal information that is related to you or to the computer is sent together with this report.

The Malicious Software Removal Tool does not use an installer. Typically, when you run the Malicious Software Removal Tool, it creates a randomly named temporary directory on the root drive of the computer. This directory contains several files, and it includes the Mrtstub.exe file. Most of the time, this folder is automatically deleted after the tool finishes running or after the next time that you start the computer. However, this folder may not always be automatically deleted. In these cases, you can manually delete this folder, and this has no adverse effect on the computer.

This section is intended for advanced computer users. If you are not comfortable with advanced troubleshooting, you might want to ask someone for help or contact support. For more information about how to contact Microsoft support, go to the Microsoft Support website.

Microsoft Download Center

You can manually download the Malicious Software Removal Tool from the Microsoft Download Center. The following files are available for download from the Microsoft Download Center:

Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help prevent any unauthorized changes to the file.

Deploying the Malicious Software Removal Tool in an enterprise environment

If you are an IT administrator who wants more information about how to deploy the tool in an enterprise environment, go to the following article in the Microsoft Knowledge Base:

Prerequisites for running the Malicious Software Removal Tool

Except where noted, the information in this section applies to all the ways that you can download and run the Malicious Software Removal Tool:

Microsoft Update

Windows Update

Automatic Updates

The Microsoft Download Center

The Malicious Software Removal Tool website on Microsoft.com

To run the Malicious Software Removal Tool, the following conditions are required:

The computer must be running a supported version of Windows.

You must log on to the computer by using an account that is a member of the Administrators group. If your logon account does not have the required permissions, the tool exits. If the tool is not being run in quiet mode, it displays a dialog box that describes the failure.

If the tool is more than 60 days out-of-date, the tool displays a dialog box that recommends that you download the latest version of the tool.

Support for command-line switches

Uses quiet mode. This option suppresses the user interface of the tool.

/?

Displays a dialog box that lists the command-line switches.

/N

Runs in detect-only mode. In this mode, malicious software will be reported to the user, but it will not be removed.

/F

Forces an extended scan of the computer.

/F:Y

Forces an extended scan of the computer and automatically cleans any infections that are found.

Usage and release information

When you download the tool from Microsoft Update or from Automatic Updates, and no malicious software is detected on the computer, the tool will run in quiet mode next time. If malicious software is detected on the computer, the next time that an administrator logs on to the computer, a balloon will appear in the notification area to notify you of the detection. For more information about the detection, click the balloon.

When you download the tool from the Microsoft Download Center, the tool displays a user interface when it runs. However, if you supply the /Q command-line switch, it runs in quiet mode.

Release information

The Malicious Software Removal Tool is released on the second Tuesday of every month. Each release of the tool helps detect and remove current, prevalent malicious software. This malicious software includes viruses, worms, and Trojan horses. Microsoft uses several metrics to determine the prevalence of a malicious software family and the damage that can be associated with it.

The following table lists the malicious software that the tool can remove. The tool can also remove any known variants at the time of release. The table also lists the version of the tool that first included detection and removal for the malicious software family.

This Microsoft Knowledge Base article will be updated with information for each monthly release so that the number of the relevant article remains the same. The name of the file will be changed to reflect the tool version. For example, the file name of the January 2005 version is Windows-KB890830-ENU.exe, and the file name of the February 2005 version is Windows-KB890830-V1.1-ENU.exe.

Be aware that the severity ratings of threats may be updated occasionally to account for changes in prevalence and other factors.

** W32/Hackdef typically hides other potentially unwanted software on the computer. If the cleaner tool reports that W32/Hackdef was detected on the computer, we strongly recommend that you run a scan with up-to-date antivirus and antispyware programs (see http://www.microsoft.com/security/pc-security/spyware-prevent.aspx). If you want to view the software that W32/Hackdef was hiding, first open the log file for the cleaner tool (%Windir%\Debug\Mrt.log). Next, in the "Possible scanning results" section, find the line or lines that note the folder in which Win32/Hackdef was found. In that same folder, you should find the Win32/Hackdef configuration file that has the .ini file name extension. View this file to determine the software that Win32/Hackdef was hiding on the computer.

To scan for and remove more malicious software, use an up-to-date antivirus product. For more information, go to the following Microsoft Protect Your PC website:

We maximize customer protection by regularly reviewing and prioritizing our signatures. Each month we add or remove detections as the threat landscape evolves.

Reporting component

The Malicious Software Removal Tool sends information to Microsoft if it detects malicious software or finds an error. The specific information that is sent to Microsoft consists of the following items:

The name of the malicious software that is detected

The result of malicious software removal

The operating system version

The operating system locale

The processor architecture

The version number of the tool

An indicator that notes whether the tool is being run by Microsoft Update, Windows Update, Automatic Updates, the Download Center, or from the website

An anonymous GUID

A cryptographic one-way hash (MD5) of the path and file name of each malicious software file that is removed from the computer

If apparently malicious software is found on the computer, the tool prompts you to send information to Microsoft beyond what is listed here. You are prompted in each of these instances, and this information is sent only with your consent. The additional information includes the following:

The files that are suspected to be malicious software. The tool will identify the files for you.

A cryptographic one-way hash (MD5) of any suspicious files that are detected.

You can disable the reporting feature. For information about how to disable the reporting component and how to prevent this tool from sending information to Microsoft, see Microsoft Knowledge Base article

Q3: Can this tool be redistributed?A3: Yes. Per the terms of this tool's license terms, the tool can be redistributed. However, make sure that you are redistributing the latest version of the tool.

Q4: How do I know that I'm using the latest version of the tool?A4: If you are a Windows 7 user, use Microsoft Update or the Microsoft Update Automatic Updates functionality to test whether you are using the latest version of the tool. If you have chosen not to use Microsoft Update, and you are a Windows 7 user, use Windows Update. Or, use the Windows Update Automatic Updates functionality to test whether you are using the latest version of the tool. Additionally, you can visit the Microsoft Download Center. Also, if the tool is more than 60 days out-of-date, the tool will remind you to look for a new version of the tool.

Q5: Will the Microsoft Knowledge Base article number of the tool change with each new version?A5: No. The Microsoft Knowledge Base article number for the tool will remain as 890830 for future versions of the tool. The file name of the tool when it is downloaded from the Microsoft Download Center will change with each release to reflect the month and the year when that version of the tool was released.

Q6: Is there any way I can request that new malicious software be targeted in the tool?A6: Currently, no. Malicious software that is targeted in the tool is based on metrics that track the prevalence and damage of malicious software.

Q7: Can I determine whether the tool has been run on a computer?A7: Yes. By checking a registry key, you can determine whether the tool has been run on a computer and which version was the latest version that was used. For more information, go to the following article in the Microsoft Knowledge Base:

Q8: Why do not I see the tool on Microsoft Update, Windows Update, or Automatic Updates?A8: Several scenarios may prevent you from the seeing the tool on Microsoft Update, Windows Update, or Automatic Updates:

Only Windows 7 users are offered the tool on Windows Update or Automatic Updates.

If you have already run the current version of the tool from Windows Update, Microsoft Update, Automatic Updates, or from either of the other two release mechanisms, it will not be reoffered on Windows Update or Automatic Updates.

For Automatic Updates, the first time that you run the tool, you must be logged on as a member of the Administrators group to accept the license terms.

Q9: How do Microsoft Update, Windows Update, and Automatic Updates determine who the tool is offered to?A9: All Windows 7 users are offered the tool if the following conditions are true:

The users are running the latest version of Microsoft Update or the Microsoft Update Automatic Updates feature.

The users have not already run the current version of the tool.

All Windows 7 users are offered the tool if the following conditions are true:

The users are not running Microsoft Update.

The users are running the latest version of Windows Update or Windows Update Automatic Updates.

The users have not already run the current version of the tool.

Q10: When I look in the log file, it tells me that errors were found during the scan. How do I resolve the errors?A10: For information about the errors, see Microsoft Knowledge Base article

891717 How to troubleshoot an error when you run the Microsoft Windows Malicious Software Removal Tool

Q11: Will you rerelease the tool even if there are no new security bulletins for a particular month?A11: Yes. Even if there are no new security bulletins for a particular month, the Malicious Software Removal Tool will be rereleased with detection and removal support for the latest prevalent malicious software.

Q12: How do I prevent this tool from being offered to me by using Microsoft Update, Windows Update, or Automatic Updates?A12: When you are first offered the Malicious Software Removal Tool from Microsoft Update, Windows Update, or Automatic Updates, you can decline downloading and running the tool by declining the license terms. This decline can apply to only the current version of the tool or to both the current version of the tool and any future versions, depending on the options that you choose. If you have already accepted the license terms and would prefer not to install the tool through Windows Update, click to clear the check box that corresponds to the tool in the Windows Update UI.

Q13: After I run the tool from Microsoft Update, Windows Update, or Automatic Updates, where are the tool files stored? Can I rerun the tool?A13: When it is downloaded from Microsoft Update or from Windows Update, the tool runs only one time each month. To manually run the tool multiple times a month, download the tool from the Download Center or by visiting the Microsoft Safety & Security Center website.

For an online scan of your system by using the Windows Live OneCare safety scanner, go to the Microsoft Safety Scanner website.

Q14: Can I run this tool on a Windows Embedded computer?A14: Currently, the Malicious Software Removal Tool is not supported on a Windows Embedded computer.

Q15: Does running this tool require any security updates to be installed on the computer?A15: No. Unlike most previous cleaner tools that were produced by Microsoft, the Malicious Software Removal tool requires no security update prerequisites. However, we strongly recommend that you install all critical updates before you use the tool, to help prevent reinfection by malicious software that takes advantage of security vulnerabilities.

Q16: Can I deploy this tool by using SUS or SMS? Is it compatible with MBSA?A16: For information about how to deploy this tool, see Microsoft Knowledge Base article

Q17: Do I have to have the previous cleaner tools installed to run the Malicious Software Removal Tool?A17: No.

Q18: Is there a newsgroup available to discuss this tool?A18: Yes. You can use the microsoft.public.security.virus newsgroup.

Q19: Why does the "Windows File Protection" window appear when I run the tool?A19: In some cases, when specific viruses are found on a system, the cleaner tool tries to repair infected Windows system files. Although this action removes the malicious software from these files, it may also trigger the Windows File Protection feature. If you see the Windows File Protection window, we strongly recommend that you follow the directions and insert your Microsoft Windows CD. This will restore the cleaned files to their original, pre-infection state.

Q20: Are localized versions of this tool available?A20: Yes, the tool is available in 24 languages. Before the February 2006 release, each localized version of the tool was available as a separate download. Starting in February 2006, the tool is now offered as a multilingual download. Therefore, only one version of the tool is available, and the appropriate language appears based on the language of the current operating system.

Q21: I found the Mrtstub.exe file in a randomly named directory on my computer. Is the Mrtstub.exe file a legitimate component of the tool?A21: The tool does use a file that is named Mrtstub.exe for certain operations. If you verify that the file is signed by Microsoft, the file is a legitimate component of the tool.

Q22: Can the MSRT run in safe mode?A22: Yes. If you have run the MSRT before you start the computer to safe mode, you can access MSRT at %windir%\system32\mrt.exe. Double-click the mrt.exe file to run the MSRT, and then follow the on-screen instructions.